Fix proposal @ https://crrev.com/2640283003.  This seems to help (i.e. before the fix the command below would see renaming of openMethodCustom, but this doesn't happen after the fix):

$ tools/clang/scripts/run_tool.py rewrite_to_chrome_style --generate-compdb out/gn third_party/WebKit/Source/bindings/core/v8/custom/V8DocumentCustom.cpp | grep MethodCustom

Before asking for CR of the fix, let me go through an automatic rename cycle to see if there are any obvious unintended consequences.

It turns out that https://crrev.com/2640283003 regresses handling of function template specializations (|to| is not rewritten to |To| on lines 347, 352, 357, 361 below):

  343 template <unsigned long sizeOfValue>
  344 int toV8SignedIntegerInternal(long value);
  345
  346 template <>
  347 int toV8SignedIntegerInternal<4>(long value) {
  348   return 123 + value;
  349 }
  350
  351 template <>
  352 int toV8SignedIntegerInternal<8>(long value) {
  353   return 456 + value;
  354 }
  355
  356 int toV8(int value) {
  357   return toV8SignedIntegerInternal<sizeof value>(value);
  358 }
  359
  360 int toV8(long value) {
  361   return toV8SignedIntegerInternal<sizeof value>(value);
  362 }

I still have to investigate what is happening here.

Hypothesis 1: getCanonicalDecl does something weird for templates
Hypothesis 2: using getCanonicalDecl messes up which AST node gets bound to "decl" id

FWIW, the skipped / not renamed decl looks as follows:

FunctionDecl 0x400a2f0 prev 0x400a5a0 </usr/local/google/home/lukasza/src/chromium4/src/tools/clang/rewrite_to_chrome_style/tests/template-actual.cc:8:1, line:11:1> line:9:5 used toV8SignedIntegerInternal 'int (long)'
|-TemplateArgument integral 4
|-ParmVarDecl 0x400a260 <col:34, col:39> col:39 used value 'long'
`-CompoundStmt 0x400a7e8 <col:46, line:11:1>
  `-ReturnStmt 0x400a7d0 <line:10:3, col:16>
    `-ImplicitCastExpr 0x400a7b8 <col:10, col:16> 'int' <IntegralCast>
      `-BinaryOperator 0x400a790 <col:10, col:16> 'long' '+'
        |-ImplicitCastExpr 0x400a778 <col:10> 'long' <IntegralCast>
        | `-IntegerLiteral 0x400a718 <col:10> 'int' 123
        `-ImplicitCastExpr 0x400a760 <col:16> 'long' <LValueToRValue>
          `-DeclRefExpr 0x400a738 <col:16> 'long' lvalue ParmVar 0x400a260 'value' 'long'

And its canonical decl is:

FunctionDecl 0x400a5a0 </usr/local/google/home/lukasza/src/chromium4/src/tools/clang/rewrite_to_chrome_style/tests/template-actual.cc:6:1, col:41> line:9:5 used toV8SignedIntegerInternal 'int (long)'
|-TemplateArgument integral 4
`-ParmVarDecl 0x400a510 <line:6:31, col:36> col:36 value 'long'

I think I will proceed with only applying hasCanonicalDecl matcher to detection of generated files, and keep using the main decl under consideration with |decl_under_blink_namespace|.  This approach passes unit tests and seems to work fine with the big rename as well.  OTOH, let me take a closer look at the remaining errors after the big rename.

This should be fixed by r445466.