BlinkGCPlugin: Handle omitted trace() in intermediary classes.

BlinkGCPlugin: Handle omitted trace() in intermediary classes.

As a result of introducing templated traceImpl() function, the callee part of
"Base::trace()" call (i.e. Base::trace) may not be fully resolved at the time
of the plugin execution. This has caused another issue in cases where trace()
is intentionally omitted because the class has no fields to trace.

Consider the following example:

    class A : public GarbageCollected<A> { trace() { ... } };
    class B : public A { /* No trace() */ };
    class C : public B { trace() { B::trace(visitor); } };

The "B::trace()" call in C is actually A::trace(). If the callee part "B::trace"
is unresolved, we only know that "there is a function call which will be
resolved to A::trace()". We still want to mark B as traced when we see such
a function call.

This patch fixes this trace call detection logic so we can handle this case.
The new logic keeps going up the class hierarchy while the class is not
required to have a trace method, and if we find a class that matches the class
of the (unresolved) callee part, we mark the direct base class of the original
class as traced.

BUG=462511
R=kouhei@chromium.org
CC=zerny@chromium.org, oilpan-reviews@chromium.org

Committed: https://crrev.com/4a636301c72b71b544b3a8acc17884e1eb8f2036
Cr-Commit-Position: refs/heads/master@{#318665}

[kouhei (in TOK), 2015-03-02 04:24:13]

lgtm

https://codereview.chromium.org/964273002/diff/1/tools/clang/blink_gc_plugin/...
File tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp (right):

https://codereview.chromium.org/964273002/diff/1/tools/clang/blink_gc_plugin/...
tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp:549: iter !=
info_->GetBases().end(); ++iter) {
Nit: use foreach?

[Yuta Kitamura, 2015-03-02 07:36:49]

https://codereview.chromium.org/964273002/diff/1/tools/clang/blink_gc_plugin/...
File tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp (right):

https://codereview.chromium.org/964273002/diff/1/tools/clang/blink_gc_plugin/...
tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp:549: iter !=
info_->GetBases().end(); ++iter) {
On 2015/03/02 04:24:13, kouhei wrote:
> Nit: use foreach?

Done.

[Yuta Kitamura, 2015-03-02 07:36:53]

The CQ bit was checked by yutak@chromium.org

[Yuta Kitamura, 2015-03-02 07:36:53]

The patchset sent to the CQ was uploaded after l-g-t-m from kouhei@chromium.org
Link to the patchset: https://codereview.chromium.org/964273002/#ps20001 (title:
"Use range-for.")

[commit-bot: I haz the power, 2015-03-02 07:37:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/964273002/20001

[commit-bot: I haz the power, 2015-03-02 08:16:13]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-03-02 08:16:51]

Patchset 2 (id:??) landed as
https://crrev.com/4a636301c72b71b544b3a8acc17884e1eb8f2036
Cr-Commit-Position: refs/heads/master@{#318665}